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Horizontal cell glutamate receptor modulation by NO: mechanisms and functional implications for the first visual
1Department of Physiology, University of Kentucky, Lexington 40536-0084, USA.
Visual Neuroscience
|June 1, 1999
Summary
Nitric oxide (NO) alters glutamate receptor function in fish retinal neurons. NO reduces receptor affinity for glutamate but increases maximal current, a cGMP-mediated effect distinct from dopamine.
Area of Science:
- Neuroscience
- Retinal Physiology
- Neurotransmission
Background:
- Horizontal cells in the retina are modulated by nitric oxide (NO).
- Glutamate receptors are key components of retinal neural networks.
- Understanding NO's role in glutamate receptor function is crucial for visual processing.
Purpose of the Study:
- To investigate the effects of nitric oxide (NO) on glutamate receptor function in isolated perch horizontal cells.
- To determine the mechanisms underlying NO modulation of glutamate receptors, including the involvement of cyclic GMP (cGMP) and dopamine.
Main Methods:
- Isolated perch (Perca fluviatilis) horizontal cells were used.
- Concentration ramp technique recorded simultaneous receptor current and agonist concentration.
- Dose-response curves for glutamate and kainate were measured with and without modulators like sodium nitroprusside (SNP), 8-Br-cGMP, cyclothiazide, and dopamine.
Main Results:
- Sodium nitroprusside (SNP) decreased glutamate receptor affinity (increased EC50) and increased maximal current (Imax).
- The cGMP analog 8-Br-cGMP increased EC50 but not Imax.
- Cyclothiazide (AMPA receptor desensitization blocker) and kainate (non-desensitizing agonist) showed that the affinity shift was independent of desensitization.
- SNP's effect on affinity was cGMP-mediated, while its effect on efficacy was distinct and synergistic with dopamine.
Conclusions:
- Nitric oxide (NO) modulates horizontal cell glutamate responses by decreasing receptor affinity and increasing maximal current.
- This modulation is cGMP-dependent and desensitization-independent.
- NO's action on glutamate receptors is distinct from, yet synergistic with, dopamine, potentially influencing visual signal transmission under varying adaptational conditions.
